Improved Depictions of the Anterior Choroidal Artery and Thalamoperforating Arteries on 3D-CTA Images Using Model-based Iterative Reconstruction.

RATIONALE AND OBJECTIVES: To evaluate the depictability of intracranial small arteries using high-resolution CTA with model-based iterative reconstruction (MBIR). MATERIALS AND METHODS: We retrospectively analyzed 21 patients who underwent brain 3D-CTA. Axial and volume-rendered (VR) images were reconstructed from the 3D-CTA raw data using adaptive statistical image reconstruction (ASIR) and MBIR. As a quantitative assessment, intra-arterial CT values of the ICA and contrast-to-noise ratio were measured to evaluate vessel enhancement. Additionally, CT values and standard deviations (SDs) of CT values and signal to noise ratio in white matter parenchyma were measured to evaluate background noise. As a qualitative assessment, the degree of vessel depictability in the anterior choroidal artery (AchoA) and the perforating branches of thalamoperforating arteries (TPA) on VR images using two different reconstruction algorithms was visually evaluated using a 3-point grading system. RESULTS: The CT value of the ICA [605.27± 89.76 Hounsfield units (HU)] was significantly increased and the SD value (i.e., image noise) of the white matter parenchyma [6.79 ± 0.81(HU)] was decreased on MBIR compared with ASIR [546.76 ± 85.27 (HU)] and [8.04 ± 1.08 HU)] (p <.05 for all). Contrast-to-noise ratio of ICA [84.48 ± 20.17] and signal to noise ratio of white matter [6.18 ± 0.75] with MBIR were significantly higher than ASIR [65.98 ± 13.08] and [5.28 ± 0.78] (p < 0.05 for all). In addition, depictions of the AchoA and TPA on VR images were significantly improved using MBIR compared with ASIR (p < 0.05). CONCLUSION: MBIR allows depiction of small intracranial arteries such as AchoA and TPA with better visibility than ASIR without increasing the dose of radiation and the amount of contrast agent.

[Application of flow-sensitive alternating inversion recovery (FAIR) to brain functional imaging].

Flow-sensitive alternating inversion recovery (FAIR), which is an excellent method of non-invasive assessment of cerebral blood flow (CBF), was applied to brain function. Because blood oxygenation level dependent (BOLD) is an established method at present, brain functional imaging by FAIR was compared with BOLD. A few minutes is the necessary scanning time in FAIR targeted for brain ischemia. For BOLD, however, scanning time in a state is several seconds. A method of improving problems with scanning time was examined. There was no problem about the stability of the signal when scanning in design method, and a similar signal change was able to be confirmed. Additionally, there was no difference between each method concerning the activated part (p > 0.05). However, the activated area in FAIR was smaller than in BOLD (p < 0.01). Brain functional imaging by FAIR offers fewer advantages than BOLD. Yet it seems that reliability increases when measurements are made by the two methods using different mechanisms.

[Potential of helical scan technique in acute cerebral infarction assessment].

The high convenience of data collection by helical scanning, such as making multi planner reformat (MPR) and shortening scan time, means that the technique is widely used to diagnose various body parts. However, non-helical scanning is still a main current for plane brain computed tomography. The possibility of diagnosing acute cerebral infarction by helical scanning MPR was examined. It was found that image degradation in helical scanning had little influence on the physical evaluation of the characteristics of modulation transfer function and the noise power spectrum, etc. In the evaluation of the ischemic change occurring at the early stage made by examination of clinical images, the result was almost equal to that obtained by non-helical scanning, as the reported sensitivity was 52% and the specificity was 95%. This suggested that brain helical scanning MPR might be applied clinically. However, a disadvantage was confirmed as helical scanning had a higher exposure dose than non-helical scanning at the start and end of scanning. The results of this study indicated that helical scanning demonstrates sufficient convenience for the assessment of acute cerebral infarction at the basal nucleus level.

CT-auto exposure control on cerebral 3D-CT angiography: dose reduction and optimized image SD for inspection purposes.

It is a fact that image noise influences for image qualities of the brain CT are known widely. The same principle applies to 3D-CTA, image noise significantly influences the depiction of blood vessels. So we evaluated the use of CT-AEC for 3D-CTA to optimize the scan dose and control the depiction of cerebral vessels by CT-AEC. We decided to optimize the noise index (NI) for cerebral 3D-CTA through the use of an imitation blood phantom. In the evaluation of the depiction of the anterior choroidal artery that was able to be confirmed with DSA, the detection rate in high resolution mode: NI 6.0 was 70%. The depiction of the anterior choroidal artery became defective in the detailed exam mode: NI 7.0, low dose mode: NI 9.0 because of the noise. As for the existence of cerebral aneurysms, the sensitivities were 100% with DSA and 94.3% with 3D-CTA in detailed exam mode, and there was no statistical difference. The specificities of 3D-CTA had lowered to 92.6% and 97.2% in DSA. In low dose mode and detailed exam mode, DLP had decreased by 55.2% and 18.1% on the average compared to a fixed tube current (P<0.05). However, in high resolution mode, DLP increased by 5.9% on the average. It was necessary to limit the scan range to the region of interest when we used a fixed tube current. This clinical research verified that CT-AEC on cerebral 3D-CTA was useful for dose reduction and control of the depiction ability for inspection purposes.

[Influence exerted by MPG-directions on diffusion tensor imaging (DTI)].

When diffusion tensor was analyzed, increasing motion probing gradient (MPG) directions and increasing signal-to-noise ratio (SNR) as result might influence diffusion tensor calculation. This study determined that mean diffusivity (MD) and fractional anisotropy (FA) are calculated by changing MPG-directions or SNR in the volunteer. There were no statistically significant differences in MD, which is calculated from all scanning parameters (p>0.05). FA of the caudate nucleus was similar as well. However, there were statistically significant differences between FA calculated from 31 MPG-directions and from 13 MPG-directions or less for the frontal lobe and caudate nucleus (p<0.05). If SNR of a trace image is 30 or more, FA wasn't affected by SNR (p>0.05). To calculate FA, minimum MPG-directions that were not statistically different compared with 31 MPG-directions were 15 MPG-directions (p<0.05).